This application is based on and incorporates herein by reference Japanese Patent Application Nos. Hei. 11-326911 filed on Nov. 17, 1999, and Hei. 11-335984 filed on Nov. 26, 1999.
1. Field of the Invention
The present invention relates to a fuel injection system supplying high-pressure fuel to an injector, which is suitable for use in a vehicle.
2. Description of Related Art
In a diesel internal combustion engine, an ECU calculates a command injection timing and a command injection amount of fuel based on an engine load such as a rotation number, an accelerate opening degree, and the like.
In a pressure accumulating fuel injection system in which a fuel is supplied from a pressure accumulating pipe to an injector, a fuel pressure inside the accumulating pipe is detected, and an ECU calculates an injection timing and an injection amount based on the fuel pressure, the command injection timing, and the command injection amount. The ECU controls to energize the injector based on the injection timing, the injection amount, and a pulse output from a rotation number sensor.
In JP-A-3-18645, as shown in FIGS. 13 and 24, a fuel pressure NPC inside an accumulating pipe is detected when an predetermined pulse is output from a rotation number sensor. An ECU calculates an injection timing including an injection timing pulse number CNECAMF and a redundant time TTMF, and an injection period TQMF based on the detected fuel pressure NPC.
That is, as shown in FIGS. 13 and 24, the ECU calculates the injection timing based on a command injection timing TFIN from a top dead center TDC and an injection delay time TDM attained based on the fuel pressure NPC. The command injection timing TFIN is attained by angle (xc2x0 CA). For example, the ECU defines the predetermined pulse as a control initial position, and calculates the injection timing from the control initial position. The ECU counts pulses from the control initial position and times the redundant time TTMF to control the injection timing.
Thus, since the ECU has to calculate the injection timing before the ECU starts to count the pulses at latest, the fuel pressure NPC inside the accumulating pipe has to be detected before the injection timing calculation. Similarly, the ECU calculates the injection period TQMF before the ECU starts the pulse count.
When a pilot injection is executed, the ECU calculates a pilot injection timing including a pilot injection timing pulse number CNECAPF and a redundant time TTPF based on the command injection timing TFIN, an interval TINT, an injection completion delay time TDEP, and a pilot injection period TQPF. Thus, since the ECU has to calculate a pilot injection period TQPF based on the fuel pressure NPC before the control initial position, the fuel pressure has to be detected before the control initial position at latest.
However, the fuel pressure inside the accumulating pipe fluctuates due to a fuel press feeding from a high-pressure fuel supply pump. Thus, especially at a transitional driving such as acceleration, a difference between a calculated injection amount and an actual injection amount from the injector arises due to a pressure difference between the detected fuel pressure and an actual injection timing fuel pressure.
For reducing the difference, in JP-A-5-125985, a fuel pressure inside an accumulating pipe is detected when an ECU stops energizing an injector, and an injection timing and an injection period at a next cylinder are calculated based on the detected fuel pressure.
However, even in JP-A-5-125985, since the calculation is one injection behind, a pressure difference between the detected fuel pressure in a previous cylinder and an actual fuel pressure in a next cylinder is increased to cause a large difference between a calculated command injection amount and an actual injection amount.
An object of the present invention is to reduce a difference between a calculated command injection amount and an actual injection amount in a pressure accumulating type fuel injection apparatus.
According to a first aspect of the present invention, an injection period is calculated based on an injection timing fuel pressure at injection timing. Thus, the injection period can be attained based on the actual fuel pressure at the injection timing. Thus, the difference between the calculated injection amount and the actual injection amount is reduced.
According to a second aspect of the present invention, a provisional injection period is calculated, and the injection period is calculated again when the injection timing fuel pressure is correctly detected. Thus, the injection amount does not abruptly change even when the fuel pressure is not correctly detected.
According to a third aspect of the present invention, a correction is calculated based on the injection timing fuel pressure, an anticipated pressure is calculated based on the correction, and the injection period is calculated based on the anticipated pressure. Thus, a difference between the calculated injection period and an actually required injection period is reduced.